Burglar alarms, fire alarms and other security monitoring alarms have become commonplace in modern society. The competition for customers, or subscribers, has become fierce among alarm service providers. Alarm service providers who can provide fast and effective alarm service at a low price have the best chance of surviving in this competitive environment. Thus, alarm service providers are searching for ways to provide cheaper, faster and more effective service to their customers.
A typical alarm system includes a subscriber terminal unit, or STU, located at the customer's premises. The STU can be connected to a number of different alarm sensors located throughout the customer's premises. The STU is connected to the alarm service provider by a telephone line. When necessary, the STU performs various tasks by sending signals to the alarm service provider and receiving signals from the alarm service provider over the telephone line. Alarm service is not possible if the telephone line malfunctions or is cut, because signals can not be sent back and forth between the alarm service provider and the STU. Therefore, most alarm service providers verify the continuity of the telephone line connected to the STU, i.e., monitor that the telephone line is operating properly, because the telephone line is critical for effective alarm service.
Systems are known for verifying the continuity of a telephone line connected to a STU. In one known system, designed for use with a twisted copper pair transmission medium, the subscriber terminal unit (STU) transmits a constant low frequency tone, or low tone (LT), over the twisted copper pair to a central office. When the LT is no longer detected at the central office, such as when the telephone line is cut, either: (1) the alarm service provider is notified that there is a problem, or (2) the central office sends a signal back to the STU to determine the problem with the STU.
Although the system described above for transmitting and monitoring a low tone works when the transmission medium is strictly a twisted copper pair, many new transmission links are digital. Problems are encountered when the transmission medium includes a digital transmission link because the low tone is filtered out. Thus, alternative systems for verifying the continuity of a customer's telephone line have been developed for use with digital loop carriers (DLCs), such as the system shown in FIG. 1.
FIG. 1 is a block diagram illustrating a known system 100 for verifying the continuity of a telephone line for use with a non-integrated digital loop system. A non-integrated digital loop system includes a digital transmission link, but the digital transmission link is terminated in a main distribution frame before reaching a switch. System 100 includes a telephone handset 105 and a subscriber terminal unit (STU) 110, each of which are connected to network interface 115 by a telephone line 117. Both telephone handset 105 and STU 110 are located at a customer's premises. Network interface 115 is connected to remote terminal 120 by twisted pair 125.
Twisted pair 125 terminates in a first line unit 130 of remote terminal 120. Remote terminal 120 is connected to central office terminal 135 by digital loop 140. A second line unit 145, located at central office terminal 135, is connected to a main distribution frame (MDF) 150 by twisted pair 155. The main distribution frame 150 is connected to a scanner 160 and a switch 165 by twisted pairs 170 and 175, respectively. Although only one scanner is shown in FIG. 1, there may be numerous scanners, associated with a number of different alarm service providers, connected to MDF 150.
As described above, when the transmission medium is strictly a twisted copper pair, a STU transmits a constant low tone (LT) over the twisted copper pair to a central office. However, when the transmission medium includes a digital transmission link, such as digital loop 140 in FIG. 1, the low tone, because of its low frequency, is filtered out at the remote terminal 120. Therefore, to overcome this problem, the system 100, shown in FIG. 1, was developed.
The system 100 shown in FIG. 1 functions as follows. STU 110 includes a low tone generator (not shown) that transmits a low frequency tone, or low tone (LT), over telephone line 117 and twisted pair 125. The first line unit 130 (LU) monitors for the low tone on twisted pair 125. Remote terminal 120 encodes a signaling bit carried between the remote terminal 120 and the central office terminal (COT) 135 over digital loop 140. The signaling bit is encoded to indicate whether the LT was or was not received by the first line unit 130.
The COT 135 monitors the signaling bit and instructs a low tone generator (not shown) in the second LU 145 either to transmit a LT or not to transmit a LT. If the signaling bit indicates that the LT was received by the first LU 130, then the low tone generator in the second LU 145 is instructed to transmit the LT. The second LU 145 transmits the LT over twisted pair 155 and twisted pair 170 to scanner 160. The scanner 160, monitored by the alarm service provider, detects the LT to verify the continuity of telephone line 117.
However, if the signaling bit indicates that the LT was not received by the first LU 130, then the low tone generator in the second LU 145 does not transmit the LT. The scanner 160 then detects that the LT is not being generated and that the telephone line 117 has been cut or is otherwise malfunctioning. The alarm service provider then initiates a telephone call to the STU 110 in an attempt to determine the nature of the malfunction.
The system 100 described above in reference to FIG. 1 functions with non-integrated digital loop carriers. However, for integrated digital loop carriers, the system 100 does not function properly because there is no central office terminal between the remote terminal and the switch to recognize the signaling bit. In addition, the switch is unable to recognize the signaling bit that indicates whether the low tone was received.
Thus, a system 200, shown in FIG. 2, was developed to monitor for line continuity when the transmission medium includes an integrated digital loop carrier. FIG. 2 is a block diagram illustrating a known system 200 for verifying the continuity of a telephone line when the transmission medium includes an integrated digital loop carrier. Telephone handset 205 and subscriber terminal unit (STU) 210 are connected to network interface 215 by telephone line 217. Network interface 215 is connected to remote terminal 220 by twisted pair 225. Twisted pair 225 terminates in a first line unit 230 of remote terminal 220. Remote terminal 220 is connected to digital cross-connect system (DACS) 235 by digital loop 237.
DACS 235 is connected to dedicated central office terminal 240 by digital loop 242. DACS 235 is also connected to switch 245 by digital loop 247. A second line unit (LU) 249, at dedicated central office terminal 240, is connected to a main distribution frame 250 by twisted pair 252. MDF 250 is connected to a scanner 255 by twisted pair 257.
In system 200, STU 210 generates a low tone (LT) that is transmitted over telephone line 217 and twisted pair 225 to first line unit (LU) 230. Remote terminal 220 encodes one of the signaling bits that is transmitted over digital loop 237 to DACS 235. The encoded signaling bit indicates whether the low tone was or was not received by the first LU 230. At DACS 235, the channels of digital loop 237 that are associated with an alarm service provider are extracted and sent over digital loop 242 to dedicated central office terminal 240.
The dedicated central office terminal 240 monitors the encoded signaling bit. If, based upon the encoded signaling bit, it is determined that the low tone was received by the first LU 230, then a low tone generator in the second LU 249 generates a low tone that is sent to MDF 250 and to scanner 255. However, if it is determined that the low tone was not received by the first LU 230, then the low tone generator in the second LU 249 is deactivated and the low tone is not transmitted to scanner 255. The scanner 255 then detects the loss of low tone and the alarm service provider connects to STU 210 via a telephone call.
The cost of system 200 is great because of the expense of equipment such as DACS 235, dedicated COT 240 and MDF 250. In addition, the systems 100 and 200 described above suffer from a lack of speed in recognizing the loss of the low tone signal. In emergency situations, a matter of seconds can be critical. Sometimes, the seconds that are lost while the scanner receives the loss of LT, recognizes it, and determines the problem can be detrimental to the effective handling of the emergency. One reason that seconds are lost is that it often takes several seconds before the loss of LT is received by the scanner because of the number of components in these systems. The scanner also requires several seconds to recognize the loss of LT. In addition, it can take several seconds for the alarm service provider to connect to the STU to query the STU and determine the problem with the STU.
Thus, there is a need in the art for a system for verifying the continuity of a telephone line that is quicker, more efficient and less expensive than prior systems.
There is a need in the art for an improved system for verifying the continuity of a telephone line for use with an integrated digital loop transmission medium.
There is a further need in the art for a system for verifying the continuity of a telephone line that does not require a dedicated central office terminal.
There is a further need in the art for a system for verifying the continuity of a telephone line that does not require a main distribution frame.